1. Field of the Invention
The present invention relates generally to a self-sustaining, continuously controlled, pyrolytic process and apparatus for the conversion of organic, non-metallic waste materials into higher quality and quantity of combustible gases, as useful energy sources. The invention includes an integrated control process and system that ensures continuous automated processes that ensure consistent energy recovery with little intervention.
2. Description of Related Art
The rapid rate of depletion of fossil fuels has made the search for new energy sources increasingly important. One of the more promising sources of new energy is green energy, e.g. biomass and other waste products which are presently being destroyed or discarded. Available space for landfills, conventionally used for disposal of these wastes, is diminishing. In addition, landfills have other shortcomings, e.g. leaching of pollutants into the ground and water tables, odors, extended time needed for refuse decomposition, and settling of the landfill site.
Incineration has been widely used as an alternative to landfill waste disposal. This is generally carried out in a combustion chamber to which air is added to accomplish combustion. Because solid waste materials vary widely in composition and moisture content, the combustion reaction is difficult to control and maintain. Incomplete combustion of the waste is common with the associated discharge of large quantities of smoke and pollution into the atmosphere. Though open air or forced air incineration of solid waste reduces waste volume, the inherent air pollution resulting is environmentally unacceptable. Incineration, even if not polluting, generates large amounts of CO.sub.2 which is undesirable.
As an environmental improvement over incineration, the pyrolytic process employs high temperatures in an atmosphere substantially free of oxygen (such as a practical vacuum) to convert organic waste to other states of matter such as a gas or vapor with an ash like residue.
Numerous pyrolysis and waste gasification systems have been proposed, however, a practical efficient system has not achieved significant commercial use. Pyrolysis has been affected in part by heat transfer problems attendant to the large variance in composition and moisture content of the waste. As to these variances in content of urban waste, statistical samples have been analyzed from diverse geographical areas beginning in the 1980's in an effort to determine its chemical and generic composition. The analysis disclosed in the table below is still considered to be valid today and generally comprises the following:
Analysis Chemical-Physical Analysis/Values in Percentages, except North- North- as indicated west east Central South Islands Italy Water 40% 41 43 49 50 44 Combustible 36 35 33 29 30 33 Materials Non-Combustible 24 24 24 22 20 23 Materials Calorific Power, 1510 1410 1330 1020 1128 1300 Keal/kg Analysis/ Percentages Sub-Filter or 18 16 18 21 13 18 Cup/Drum Screen Cellulosic Matter 25 23 23 16 20 22 Plastic Matter 9 7 6 7 8 7 Metals 3 3 3 2 2 3 Inert Materials 8 9 9 5 8 7 Organic Matter; 37 42 41 49 49 46 Various
Because municipal waste contains significant amounts of plastic that melt before burning, such waste tends to quench the combustion and can eventually stop the pyrolytic gasification process entirely. Large amounts of smoke and other pollutants generated by this inability to adequately control the combustion of waste material which are emitted into the atmosphere have compromised the commercial utility of the gasification process.
Incomplete or marginal pyrolysis is unreliable in continuous operation. Even employing complicated and expensive procedures for capturing the smoke and other pollutants, inadvertent emissions of large amounts of these pollutants remain common.
For example, to achieve relatively steady state operation when gasifying common municipal waste, temperatures for pyrolysis must be used which approach the temperature at which slagging of inorganic material occurs within the pyrolysis chamber. The temperature in the pyrolysis chamber often rises above the slagging temperature due to the difficulty in maintaining the temperature within the pyrolysis chamber. The inorganic components of the waste melt form a tenaciously adhering slag coating on all surfaces exposed to the waste. Variances in content and moisture of municipal waste make controlling the pyrolysis temperature below the slagging point extremely difficult.
Prior devices and processes have not adequately addressed these problems which must be dealt with on a continuously changing basis. Accordingly, it would be a significant advancement in the art to provide a method and apparatus which is self-sustaining, and simultaneously controls sorting, drying, distillation, cracking, purification, and pollution while significantly reducing waste and recovering substantial amounts of energy from the waste. Such process and apparatus for the conversion of waste materials are disclosed herein.